1. Field of the Invention
The present invention relates to an electronic device including a circuit using a photosensor and a transistor. For example, the present invention relates to an electronic device using, as its component, an electro-optical device typified by a liquid crystal display panel utilizing a touch panel.
2. Description of the Related Art
A CMOS sensor is used mostly in digital cameras or cellular phones and has an important imaging function. A CMOS sensor is a photosensor utilizing an amplifying function of a MOS transistor, and can be manufactured by a general CMOS process. In addition, a CMOS sensor requires lower driving voltage than a CCD sensor and thus leads to low power consumption of a solid-state imaging device.
A display device using a touch sensor is attracting attention. A display device using a touch sensor is called a touch panel, a touch screen, or the like (hereinafter also referred to simply as a touch panel). A touch panel is used mostly in personal computers or cellular phones and allows image display and operation to be done on the same panel. Patent Document 1 discloses a display device using an optical touch sensor.
A CMOS sensor performs three operations: storage of charge generated by a photodiode, read-out of the charge, and reset of the charge. In performing these three operations, a CMOS sensor uses a node that stores charge resulting from photocurrent generated by a photodiode (such a node is hereinafter referred to as an FD), and wire for supplying a control signal. Patent Document 2 discloses a structure of a solid-state imaging device with a layout that allows the potential of such an FD storing charge to be insusceptible to fluctuations in the potential of a signal line.